The present invention relates generally to heat rejection systems, and more particularly to solid state heat rejection systems for use in space.
Systems designed for operation in space often require heat rejection capabilities. For instance, space vehicles and satellites often utilize photovoltaic power systems that can generate waste heat. Photovoltaic systems utilizing solar concentrators can generate particularly large amounts of waste heat. It is desirable to provide for rapid transfer of thermal energy for dissipation, and to accommodate the transfer of relatively large amounts of thermal energy. However, there are numerous difficulties in providing suitable heat rejection.
Systems designed for operation in space must be able to be launched to an orbital or sub-orbital altitude. For satellite systems, this generally involves storage within a launch vehicle payload fairing prior to deployment in space. Launch vehicle payload fairings provide limited payload space, often as a conical or bell-shaped volume. Therefore it is desirable for heat rejection systems to be relatively compact (i.e., to occupy a relatively small volume) when stowed for launch.
Launch vehicles and their fuels are highly expensive, and are frequently expendable. Therefore, it is also desirable to reduce the mass of launch payloads, in order to help reduce the size and cost associated with the launch vehicle. In this context, the mass of heat rejection systems is important. Heat rejection systems that would otherwise operate suitably once in space may be unworkable for practical applications because they would add too much mass to the launch vehicle's payload. There may even be a maximum feasible mass limit imposed upon heat rejection systems for some applications.
Additional difficulties limit heat rejection systems. Such systems must be able to function in a zero- or low-gravity environment. It is also desirable for heat rejection systems to have a wide thermal operation range, and to limit failure modes. Some prior art systems utilize two-phase heat pipes, which transfer thermal energy between condenser and evaporator sections using a working medium that changes back and forth between liquid and gaseous states during operation. However, those prior art systems are heavy and bulky, particularly due to the evaporator and condenser sections, and can cease functioning in certain temperature ranges, such as if the working medium freezes. Those systems can also require undesirably complex internal mechanisms to ensure proper functioning in a low-gravity environment, for instance, requiring active working medium pumping systems.